docs: def _prefix_from_prefix_int(self, prefixlen):
          """Validate and return a prefix length integer.
  
          Args:
              prefixlen: An integer containing the prefix length.
  
          Returns:
              The input, possibly converted from long to int.
  
          Raises:
              NetmaskValueError: If the input is not an integer, or out of range.
          """
          if not isinstance(prefixlen, (int, long)):
              raise NetmaskValueError('%r is not an integer' % prefixlen)
          prefixlen = int(prefixlen)
          if not (0 <= prefixlen <= self._max_prefixlen):
              raise NetmaskValueError('%d is not a valid prefix length' %
                                      prefixlen)
          return prefixlen